Stackable thin walled tubs



- Nov. 10, 1970 L. s. MOUNTS ETAL 3,539,552

STACKABLE THIN WALLED TUBS Filed March .L7, 1969 may 5 J W M n m /.R m MT f Patented Nov. 10, 1970 3,539,552 STACKABLE THIN WALLED TUBS Lewis S.Mounts, Midland, and Ruben A. Tigner, Bay

City, Mich., assignors to The Dow Chemical Company, Midland, Mich., acorporation of Delaware Filed Mar. 17, 1969, Ser. No. 807,843 Int. Cl.B65d 21/02 US. Cl. 220-97 9 Claims ABSTRACT OF THE DISCLOSUREDESCRIPTION OF THE INVENTION Containers as are customarily used forluncheon meat vacuumized packaging applications are commonly of a lidand tub variety. The tubs are normally thermoformed from clear plasticsheet material placed across the mouth of a suitably configured moldcavity, and formed into the cavity by vacuum drawing, usually with plugassist techniques. The draw can be shallow or deep, i.e., 1 to 4 inches.Even for the more shallow draws, the heated sheet material as it isformed into the mold cavity usually stretches and thins considerably.For example, it is not uncommon for mil thermoplastic sheet, formed intoone inch deep tubs, to drawn down to 3 to 6 mils in thickness in variousregions of the tubs so formed, particularly in the side wall sections ofthe tubs where the drawing is normally most severe.

Accordingly, for thin walled containers of this sort, it has beendifficult to construct into such containers effective stacking featuressince inflections and distortions in such thin walled material occurunder relatively slight loads.

In the past, it has been customary to locate such stacking features inthe peripheral regions of the tub where thinning is usually at aminimum. For example, the tub can include a top wall, a downwardlydepending side wall, and a horizontally disposed flange member integralwith the lower extent of the tub side wall. The flange normally carriesa hollow downwardly extending tongue which is adapted to be received ina marginally disposed groove formed in the lid part of such containers.A stacking feature is obtained by reverse sloping the tongue, that is,by sloping it inwardly such that when the tubs are stacked, the tonguerests on the inner extent of the flange member of the tub directlytherebelow in the stack.

The aforedescribed stacking feature is less than totally effective inpreventing containers from looking or jamming together in a stack. Theflange member in which the tongue is formed does have considerableflexibility. Accordingly, the tongue tends to bend in a moment about thehorizontal plane of the flange member, particularly if the tub isrectangular, as opposed to circular, in shape. Thus, under a load thetongue can slip outwardly and off the inner extent of the flange memberand lock into the hollow upper part of the tongue member of the tubtherebelow in the stack.

The prior art has also experimented with raising sections of the topwalls of such containers to obtain an effective stacking feature. Forexample, a hollow up wardly extending bead generally integral about themarginal edge of the top wall can be employed to this end. The jammingof the lower such head into the hollow underside of the one thereabovein a stacked arrangement of such containers, however, is a problem evenif reverse sloping principles are employed, and, accordingly, theeffectiveness of such a stacking feature is oftentimes less thandesired.

It is an object of the present invention to provide an improved stackingfeature for thin walled tub containers employed in vacuumized luncheonmeat, cheese, and like packages.

It is a further object of the present invention to provide such astacking feature wherein the same is located in the side wall sectionsof such a tub.

It is yet a further object of the present invention to strategicallylocate and construct such stacking features in such a manner as tominimize the effect of inflections and distortions in the containerwalls which tend to cause the containers to jam or lock together in thestack.

Briefly, then, the present invention contemplates an improved stackingfeature for usage in light or thin walled preformed plastic tubs ofself-supporting structure. Such tubs normally include a top wall and aside wall depending downwardly and outwardly therefrom and terminatingin an outwardly flaring or horizontally disposed flange member. Thelatter carries a mating region as, for example, a downwardly extendinghollow tongue. The stacking feature comprises a plurality of hollowshoulders, each including a generally horizontally disposed first partextending outwardly from a mid-region portion of the side wall, and areverse sloped second part extending diagonally inwardly from adjacentthe outermost extent of the first portion and merging with the side wallat its junction with the horizontally disposed flange member. Suchshoulders are set in a vertically corrugated background wherebyinflection under load in the thin material of such containers iseffectively avoided to the extent that a workable jam-resistant stackingfeature is provided. For rectangular containers, such stacking shouldersare strategically positioned at corner regions of the side wall wherebythe rigidity in such corner regions in combination with the indicatedcorrugated background provides an especially effective stacking feature.

Other objects and advantages of the present invention and its details ofconstruction will be apparent from a consideration of the followingspecification and accompanying drawings wherein:

FIG. 1 is a top view of a tub including a stacking feature constructedaccording to the principles of the present invention;

FIG. 2 is a side view of the tub of FIG. 1;

FIG. 3 is an enlarged broken cross-sectional view of the tub of FIG. 1in stacked relationship with another such tub; and

FIG. 4 is a cross-sectional view taken along reference line 4-4 of FIG.2.

Referring now more particularly to the drawings, there is shown in FIGS.1 and 2 a shallow generally rectangularly shaped tub 10 including a topwall 12. A side wall 14 is peripherally integral with top wall 12 anddepends downwardly and outwardly therefrom at an angle a with thevertical axis 16, as is denoted in FIG. 3.

Tub 10 further includes a peripherally continuous flange portion ormember 18 extending generally outwardly adjacent the lower extent 20 ofside wall 14 and terminating in a rectangularly defined boundary 22.Intermediate the boundary 22 and the lower extent 20 of the side wall14, flange carries a downwardly extending hollow tongue member 24.Tongue member 24 is adapted to be received in a marginally disposedgroove of a suitable lid member (not shown). Such a lid is preferably aplastic film and foam laminate as, for example, taught in commonlyassigned US. atent application Ser. No. 639,213, filed May 17, 1967, inthe name of Ruben A. Tigner, a co-inventor of the present invention, thedisclosure of which is fully incorporated herein by reference.Alternately, of course, more conventional lids such as those formed ofimpermeable paperboard, plastic, metal or the like can be adapted tousage in combination with tub 10.

As mentioned above, the inventive concept relates to a stacking featurefor tub 10, and to this end there is provided a plurality of stackingshoulders 26 located in the lower regions of side wall 14.

As is best shown in FIG. 3, each stacking shoulder 26 comprises agenerally horizontally disposed first member or part 28 extendingoutwardly from the side wall 14 at a location intermediate of top wall12 and flange 18, and a reverse sloped second member or part 30extending diagonally inwardly and downwardly from the outermost extentof the first part 26. Diagonal part 30 merges with the side wall 14 atthe lower extent 20' thereof adjacent flange member 18.

Referring again to FIG. 3, the following critical dimensions are setforth in the drawings wherein A represents the vertical height of thestacking shoulders 26, B represents its horizontal dimension, and Crepresents the vertical extent of tongue member 24.

Correspondingly, Y represents the inner surface to inner surfacedimension of tub 10 as measured from the lower terminating ends 25 oftransversely opposed or aligned diagonal members 30, and X representsthe same dimension, only as measured from a point on the inner surfaceof Side wall 14 adjacent the first parts 28 of shoulder 26.

The angular dimensions critical to the proper formation of shoulders 26are which represents the slope of diagonal part 30 with respect to thevertical axis 16 and, as mentioned above, 00 which represents the slopeof side wall 14 with respect to the same axis.

In order for stacking shoulders 26 to perform properly, the followingrelationships between the above-indicated dimensions, both angular andrectilinear, must be observed in constructing shoulders 26:

(1) sine u A side wall 14 thickness (2) Y X +2 (side wall 14 thickness)(3) Y X+2B+2 (side wall 14 thickness) Referring now to FIG. 4, there isshown a corrugated pattern 32 which represents a cross section throughside wall 14 of tub 10. The corrugations as shown in FIG. 2 arepreferably vertically aligned with a hill to valley dimension E in therange of approximately 15 to 100 mils, as measured at the region of sidewall adjacent first part 28 of shoulders 26.

The corrugations of corrugated pattern 32 of side wall 14 in combinationwith the strategic location of shoulders 26 at corner regions 34 is bestshown in FIG. 1, effectively prevents inflections and distortions whichwould cause the shoulders to slip over one another and thereby causejamming or locking of such containers in a stack, as is explained morefully hereinafter.

In FIG. 3, first parts 28 of shoulders 26 are illustrated as beingsubstantially horizontal. However, in thermoforming of tub 10, it isdiflicult to obtain perfect detail and oftentimes shoulders 26 willslant downwardly and outwardly somewhat, rather than reside in a truehorizontal plane. Considerable rounding of the corners 36 of shoulders26 is also difiicult to avoid and does affect the load bearingcharacteristics of such shoulders.

However, by incorporating shoulders 26 adjacent to corner regions 34 andby employing corrugated patterns 32 to rigidify the side walls againstinflections and distortions as described above, excellent stackingcharacteristics are obtained by the stacking shoulders 26 constructiontaught herein as exemplified by the following example.

EXAMPLE A 10 mil polyvinyl chloride thermoplastic sheet material isplaced over the mouth of the cavity. A vacuum draw and heated plugarrangement is employed to form the sheet to the mold whereby a tub of.922 inch in depth having a configuration substantially conforming tothat shown in the drawings is obtained. The tub is removed from the moldand examined and the following approximate dimensions are recorded:

(1) oc-5 40 minutes (3) A-.180 inch (4) B.036 inch (5) C-.125 inch (6)D.5 inch (7) E-31 mils (8) X and Y4.089 and 4.125 inches, respectively.

To test the stacking capabilities and effectiveness of such tubs, twelvesuch tubs were stacked, and a five-pound weight placed on top of thestack. The weight remained in its position for a duration of one minute.The weight was then removed and the containers inspected. No jamming orlocking together of such containers was observed. Measurements made inthe side wall 14 regions of such tubs varied from a low of approximately3.5 mils to a high of approximately 6 or 7 mils.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in the art that various changes and modifications can be madetherein without departing from the spirit and scope of the invention.

What is claimed is:

1. In a light-walled plastic tub of a type for use in a vacuum package,the tub having a top wall and a side wall peripherally integral with thetop wall and depending generally downwardly and outwardly therefrom, andincluding a peripherally continuous flange member extending generallyoutwardly from adjacent the lower extent of the side wall, an improvedstacking feature comprising: a plurality of stacking shoulders formed insaid side wall, each such shoulder comprising a first part extendinggenerally outwardly from said side wall at a location intermediate saidtop wall and said flange member, and a reserve sloped second partextending diagonally downwardly and inwardly from adjacent the outermostextent of said first part, said shoulders being set in a corrugatedbackground comprising repetitive hill and valley regions formed in saidside wall at locations generally immediately above said first parts,respectively, whereby distortion of the side wall under load isminimized in the regions of said shoulders, the hill to valley dimensionof said corrugated patterns as measured adjacent said first parts, beingless than mils.

2. The tub of claim 1 wherein said side wall is generally rectangular inshape, said stacking shoulders being disposed adjacent the cornerregions of said side wall.

3. The tube of claim 2 wherein each of the four sections comprising saidside wall include two stacking shoulders, said shoulders being disposedin the outermost one-third portions thereof adjacent the two oppositecorner regions, respectively, associated with each of said sections.

4. The tub of claim 1 wherein said flange member includes a mating meanshaving a vertical dimension, the vertical height of said shoulders beinggreater than said vertical dimension.

5. The tub of claim 1 wherein said repetitive hill and valley regionsare aligned substantially in the vertical direction.

6. The tub of claim 5 wherein said hill to valley dimension is in therange of from about 15 mils to 100 mils.

7. The tub of claim 1 wherein said second part of said shoulders mergeswith said side wall adjacent the juncture of the side wall and saidflange member.

8. The tub of claim 6 wherein the maximum thickness of said side wall asmeasured in a mid-region portion thereof is less than 7 mils.

6 9. The tub of claim 6 wherein the thickness of said side wall is inthe range of from about 3.5 mils to about 7 mils.

References Cited UNITED STATES PATENTS 2/1967 Luker. 6/1967 Ringlen.

